The present invention relates to a system for detecting clogged filters in variable air volume air conditioning sytems.
Any building whether residential or commercial having forced air systems for heating and cooling the interior of the building has a requirement for a filter to take out of the air being delivered to the interior of the building any dirt or airborne foreign particles. Either the filters are commercially available fiber glass filters which require periodic replacement or electrostatic air cleaners which require periodic cleaning. In order to replace or clean the air filter when it is dirty, the owner or maintenance personnel of the building must rely upon either their own memories or some sort of an automatic follow up system in order to avoid waiting too long for the replacement or cleaning of the air filter. Dirty air filters, as is well known, impede the air movement of the heated or cooled air throughout the building thus raising the energy costs of maintaining the desired temperature within the building.
There have been automatic systems for detecting clogged air filters which typically involve sensing the pressure drop across the air filter. As the air filter becomes dirty, the static pressure across the air filter begins to increase for any given air velocity moving through the duct in which the air filter is located. Simply using the pressure drop across the air filter in this type of air conditioning system is sufficient to determine whether or not there is a clogged filter for constant volume systems.
In variable air volume systems, however, the pressure drop across an air filter will vary according to the air volume moving through the duct in which the air filter is located in response to varying air flows. Thus, the detection of a change in the pressure drop across an air filter does not necessarily mean that the air filter has become clogged but may mean that the velocity of air moving through the duct has changed.